In the field of high-energy or particle physics it is highly desirable to monitor the power level that is produced by a particle accelerator.
An electron radiates with a wide spectrum when it is bent through a dipole, the so-called Synchrotron Radiation (SR). In most cases the SR power is proportional to number of electrons per bunch. However, if the bunch length of the radiating electron beam is short compared to the SR wavelength, the individual electrons radiate in phase and SR power becomes proportional to the square of the number of electrons per bunch, the so called Coherent Synchrotron Radiation (CSR). At long wavelengths the CSR power is enhanced by a large factor proportional to the number of electrons per bunch, with the factor typically in the range of 10.sup.6 to 10.sup.10. The CSR power has a strong dependence on the longitudinal density distribution, or the bunch length, of the beam.
CSR was theoretically investigated long ago and was first observed in a linear accelerator in 1989. The CSR power can be expressed as: EQU P.sub.CSR (.lambda.)=P.sub.inc (.lambda.)*(1+NF(.lambda.)) (1)
where P.sub.CSR and P.sub.inc are the coherent power and the incoherent power, respectively, N is the number electrons per bunch, and F is a form factor given by: EQU F(.lambda.)=(abs.intg.S(z)e.sup.-2.pi.iz/.lambda. dz!}.sup.2( 2)
where normalized S(z) is the longitudinal density distribution.